The present invention relates to a heat-sensitive recording head used in a facsimile printer or the like. More particularly, the invention relates to a matrix wiring arrangement in such a recording head.
In a conventional heat-sensitive recording head of the general type to which the invention pertains, especially in a recording head intended for line scanning, the drive leads correspond to the recording positions in the ratio of 1:1. That is, one drive lead is provided for each recording position. Because of this construction, the conventional recording head suffers from a problem that, when it is required to provide a head which is capable of carrying out recording operations with a high recording density and quality, it is difficult to connect the leads to the drive circuit because the distance between adjacent leads is considerably short.
In order to overcome the above-described difficulties, a heat-sensitive recording head as shown in FIG. 1 has been proposed in the art. In FIG. 1, reference numeral 1 designates a ceramic plate or substrate which is constructed by attaching a heat sink of aluminum or copper to a ceramic plate so as to provide excellent heat resistance characteristics and to provide a heat sink action. Reference numeral 2 designates a number of heat generating elements at different recording positions. The heat generating elements 2 are made of thin or thick film material or are fabricated by a semi-conductor technique. The surfaces of the heat generating elements 2 are covered by a protective layer of glass or the like in order to improve the wear resistance characteristic of the head. Further in FIG. 1, reference numerals 3 and 4 designate two lead groups which are composed of a number of leads a.sub.1 through a.sub.n and a number of leads b.sub.1 through b.sub.n, respectively, which supply currents to the heat generating elements 2. The leads are arranged alternately on both sides of the heat generating elements 2 in such a manner that the array of heat generating elements 2 is divided into a number of segments, the size of which determines the recording density with the segments being located between the leads 3 and 4.
Because of the above-described arrangement, the heat-sensitive recording head of this type is termed an "alternate lead type" heat-sensitive recording head. As the recording head has a number of alternately arranged leads which act as common leads between adjacent recording positions, this device is advantageous in that the distance between terminals to be connected to the drive circuit, that is, the distance between adjacent leads, is twice the recording density and the alignment of the leads with the heat generating elements can be readily achieved.
As in the above-described conventional head, the head is provided with a plurality of heat generating elements and a matrix drive technique is employed therefor. Furthermore, as the heat response characteristic of the heat-sensitive recording head is relatively low, a number of heat generating resistors are generally provided and plural heat generating resistors are simultaneously driven. In addition, matrix wiring and reverse current blocking elements are provided for the heat-sensitive recording head. This will be described with reference to FIG. 2 in more detail.
In FIG. 2, reference numeral 1 designates a supporting substrate of aluminum or the like having high electrical and heat resistances, 2 heat generating elements, 3 common drive electrodes, 4 individual leads, 5 common drive leads, 6A and 6B reverse current blocking elements such as diodes, 7 matrix drive leads, 8 common drive terminals (or terminals B), and 9 individual lead terminals (or terminals A).
As shown in FIG. 2, the reverse current blocking elements 6A and 6B are connected to the leads 3 and 4, respectively. Accordingly, the number of reverse current blocking elements must be equal to at least the number of heat generating elements. Therefore, the reverse current blocking elements represent a considerably large part of the heat-sensitive recording head in both circuit elements and space as well as manufacturing cost. Furthermore, the number of connections between the reverse current blocking elements 6A and 6B and the leads is at least twice the total number of heat generating elements. The great number of connections inversely affects the reliability of the heat-sensitive recording head.
Accordingly an object of the present invention is to greatly reduce the total number of reverse current blocking elements compared with a conventional heat-sensitive recording head or to eliminate the reverse current blocking elements entirely thereby decreasing the manufacturing cost of the heat-sensitive recording head and to improve the reliability thereof.